Considering that a fraction is not defined when the denominator is zero, the equation is not defined for an angle of 90º.
<h3>When is a fraction not defined?</h3>
A fraction is not defined when the denominator is zero.
In this problem, the expression is given by:
cos(θ)/(1 - sin(θ)) + cos(θ)/(1 + sin(θ)) = 4.
The denominators are zero in two cases:
- 1 - sin(θ) = 0 -> sin(θ) = 1 -> θ = 90º.
- 1 + sin(θ) = 0 -> sin(θ) = -1 -> θ = 270º.
Hence the equation is not defined for an angle of 90º.
More can be learned about not defined fractions at brainly.com/question/16948935
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